Wind turbines have received increased attention as a renewable energy source for generating electricity. In a conventional wind farm, a plurality of wind turbines can be arranged in one or more clusters. Each cluster can include a plurality of wind turbines connected to a collection system, such as a 33 kV collection system. In a typical configuration, a doubly fed induction generator (DFIG) wind turbine can include a rotor and stator. The rotor can be configured to generate electricity at a first voltage, such as 690 V, and the stator can be configured to generate electricity at a second voltage, such as 6 kV. A power converter can be coupled to the rotor, which can convert the power from the rotor and provide it to an auxiliary winding on a three-winding transformer. The three-winding transformer can have, for example, a 33 kV primary winding coupled to the collection system, a 6 kV secondary winding coupled to the stator, and a 690 kV auxiliary winding coupled to the power converter, and can be configured to convert power from both the rotor and stator to a 33 kV AC power. The collection system, such as a 33 KV collection system, can be coupled to the primary winding of each three-winding transformer in a cluster of wind turbines, and can provide the power from one or more clusters to a grid-connected transformer. The grid connected transformer can convert the power to a voltage suitable for transmission on a transmission system.
During operation of the wind farm, wind conditions, such as speed and direction, may vary over time. For example, the wind speed can vary between periods of normal operation, such as winds of 5 m/s or greater, to periods of low-wind conditions, such as winds of less than 5 m/s. During low-wind conditions, the rotor speed of a DFIG may drop, and the power converter may not be able to stay connected to the rotor winding if the slip speed (i.e., the difference between the synchronous frequency and the rotor speed converter into electrical frequency) dips below a slip speed threshold. This slip speed threshold can be due to the rating of power semiconductor devices (e.g., MOSFETs) in the power converter. When this occurs, a system protection scheme may be triggered, which can shut down the DFIG and prevent power production during low-wind conditions.